The present invention relates to controlled release compositions comprised of porous polymeric particles of microscopic dimensions, retaining within their pores various types of impregnants useful as active ingredients for a wide variety of medicinal, cosmetic, and other utilitarian and esthetic purposes
Controlled release formulations consisting of porous particles of an inert solid material with active substances retained in the pores are disclosed in Won. U.S. Pat. No. 4,690,825, issued Sept. 1, 1987, and pending application Ser. No. 91,641, filed Aug. 31, 1987 (commonly assigned herewith) The active ingredients are generally liquid in form, retained inside the pores of the particles by capillary forces. The pores are interconnected and open to the particle surface, permitting full diffusion outward of the retained active ingredients. In some cases, the formulation consists solely of the particles, and in others the formulation consists of a dispersion of the particles in a suitable vehicle to resemble conventional skin preparations such as liniments, gels, lotions or ointments. In either case, release of the active ingredient from the pores is controlled by diffusion. although release upon demand is achieved by agitation or rubbing of the formulation.
The particles disclosed in the patent and application referenced above are generally rigid in character, limiting their usefulness to applications where high pressures are not encountered, and where a small degree of frictioin and abrasion caused by rigid particles is not a problem.